Sen. John McCain’s malignant brain tumor, which was removed on Friday, has prompted questions about the kind of cancer he’s fighting. The Daily News looked to the American Brain Tumor Association and Andrew S. Chi, M.D., head of neuro-oncology at NYU Langone’s Perlmutter Cancer Center, for answers.

What is glioblastoma?

Glioblastoma is aggressive and quick-spreading due to its association with a large network of blood vessels in the brain.

What causes it?

The exact cause of glioblastoma is unknown, but they arise from gluey supportive tissue of the brain. McCain has had melanoma, but, says Chi, “there is no clear link between melanoma and glioblastoma.”

There’s some speculation that McCain’s brain tumor may have been linked to his wonky questioning during congressional testimony last month by former FBI Director James Comey.

What’s the next treatment step?

John McCain, who's famous for being a fighter, is seen here in a 2000 photo after he underwent surgery to remove skin cancers.

(Win McNamee/REUTERS)

A statement from McCain’s office noted that doctors believe they removed all of the tumor tissue, but microscopic pieces can remain. “Glioblastoma sends out fingers deep into the brain,” says Chi. “There will always be cells that move beyond the borders of what you can see on an MRI. That’s one reason why it’s so deadly.”

Radiation and chemotherapy could be used to attack any such cells, but adds, Chi, glioblastomas "are inherently resistant to radiation and chemotherapy."

What is the prognosis?

The median survival rate is about 14 months to three years. One study found that 10% of patients live five years or more.

Having the best care won’t hurt the senator’s chances. And McCain, who underwent surgery at the Mayo Clinic, No. 1 in the nation for neurology and neurosurgery, will get the best treatment.

The senator also won't break the bank getting treated. Unlike most Americans, members of Congress have excellent health insurance plans.